In the silicone coatings industry, siloxanes are applied by means of rollers to sheet substrate materials such as film or paper. In order to raise the productivity, there is a trend towards increasing the machine speed. Spray mists are formed on the silicone applicator units at belt speeds of more than 300 m/min. The misting results in a loss of coating material, and the ambient air becomes loaded with the spray mist. The formation of spray mist can be reduced by the addition of anti-misting additives.
Silicone release coatings are cured either thermally or by radiation. With radiation curing, a distinction is made between cationic or free-radical polymerization. Available commercially are, for example, anti-misting additives, or silicone mixtures including anti-misting additives, for thermally curing silicone release coatings. Thermally curing silicone release coatings are generally mixtures comprising hydrosiloxanes and vinylsiloxanes, which by the transition metal-catalyzed hydrosilylation are crosslinked and thereby cured. The anti-misting additives used for these systems are typically characterized in that they comprise particularly high molecular mass siloxanes which through residual functionalities, are able to be incorporated by curing as well.
The preparation and use of anti-misting additives for thermosetting silicone release coatings are described for example in EP 1481018 and EP 1277786 and also in U.S. Pat. No. 6,956,096. These prior art anti-misting additives comprise branched siloxane polymers obtained by linking alkenyl groups with SiH groups.
U.S. Pat. No. 6,774,201 presents star-branched siloxane polymers which are obtained by hydrosilylation.
All of the anti-misting additives described above have in common that they have been developed for specifically thermally curing silicone release coatings. The prior art anti-misting additives however are not in tune with the particular requirements of UV-curing silicone release coatings in relation, for example, to anti-misting effect, release force, adhesion and crosslinking, force of subsequent adhesion, and ageing.